In the 1930-1940
several design teams came up with idea of a new class of aircraft - "Tjazholij Krejser"
(Heavy Cruiser). This had to be a modification of production bomber with enormous defensive
firepower. It supposed to fly in formation with (similar in design) bombers and repel attacking
fighters.

And for good - later in WWII some USAF B-17's were tried same way - with increased firepower and ammo. Experience was
negative, because Luftwaffe pilots easily 'calculated' such a "Heavy Cruisers" and brought them down first, leaving the
rest of bombers (with armament decreased in favor of bomb load) unprotected. Only conventional fast long range escort
fighters could provide bombers with reasonable protection.